One of the methods used for watering of plants, trees and other growing things is to flow water through a length of tubing, commonly referred to as a dripline. A dripline is typically comprised of small diameter plastic tubing, which has spaced apart water discharge points, or emitters, along the length of its sidewall. Watering of plants is most often accomplished by running a drip line at a shallow depth beneath the soil surface; alternately, the dripline is run along the surface of the earth. Running along the surface provides flexibility in re-positioning the lines and minimizes installation costs. Burial protects the lines from damage due to surface maintenance and use.
There is an obvious problem with respect to evenness of water distribution along the length of a dripline conduit, for instance one of 50 feet or more in length, if the spaced apart ports in the tubing are all the same diameter. Line loss in the tubing will mean there will be greater pressure and flows at points near the feed end than at the far end. Variation in earth-surface elevation or depth of burial will create pressure variations in a dripline. To address these factors, certain commercial products have pressure compensating exit ports, or emitters, at the locations where the water discharges. Commercial examples include Rainbird™ LD-06-18-500 tubing (Rainbird, Inc., Azusa, Calif.) and Part No. 08-WRAM.6-24V tubing (Netafim USA, Fresno, Calif.). Typically, such emitters throttle water flow, to make it independent of pressure, so long as pressure in the dripline by the emitter is above a certain threshold, for example, above 5 pounds per square inch gage (psig). See U.S. Pat. No. 5,628,462 to Miller, and product literature of the aforementioned manufacturers, about pressure compensating emitters.
When water flows through the emitters of a buried dripline into the soil, the water disperses according to the characteristics of the soil. In typical soils there is a localized concentration of water near the emitter, whereas it is preferable that the water be dispersed. The present invention is founded on the observation that, where soil is saturated on a persistent basis, dripline irrigated soil will have inferior conditions for vegetative root growth. In particular, there will tend to be a resultant localized deficit in oxygen. In other respects, as a corollary, the local composition of soil gas maybe quite different from atmospheric air, and quite different from areas remote from the emitter region. Furthermore, if the water being distributed contains organic substances, especially fertilizers, or if the water is wastewater, having a biological and or chemical oxygen demand, then the organic materials in those waters can accumulate in vicinity of the emitters, to the extent of making the soil condition adverse to plant growth. Thus, commercial driplines and practices present limitations, which if overcome can present better growing conditions and better capacity to utilize wastewater.
In the prior art, air has been flowed through soil to enhance conditions in the soil, to improve plant growth, for instance in the turf of golf greens, sports fields, and the like. See U.S. Pat. No. 6,018,909, Subsurface Soil Conditioning to Potts, applicant herein, and the references cited therein. Driplines have been used to add oxygen for crop growing purpose, by mixing atmospheric air into the water as it is flowed into the dripline, to enhance the amount of oxygen carried by pressurized water in the dripline. See U.S. Pat. No. 6,173,526 to Mazzei.